The present invention relates to a self-advancing film cassette for advancing the leader of a photographic film strip in accordance with rotation of a spool, and more particularly to an improved self-advancing film cassette which is capable of separating the film leader from a film roll wound on a spool with high reliability.
Presently, a film cassette containing a roll of photographic film strip of 135 type (35 mm in width) is used most widely. This film cassette is constituted by a light tight cylindrical cassette shell provided with a film passage mouth, a spool rotatably contained in the cassette shell, and a film roll coiled on the spool. The film leader protrudes from the film passage mouth. When loading the film cassette into a camera, the film leader is brought into engagement with a threading member of the camera. By driving the threading member, the film is pulled out from the cassette shell and fed to a film take-up chamber so as to be wound onto a take-up spool in this chamber.
In recent years, in order to meet a demand for making the film cassette compact and easy to handle, a self-advancing film cassette has been proposed in which the entire film is contained in the cassette shell and the film leader is advanced from the film passage mouth in accordance with rotation of the spool. FIG. 25 shows a schematic view of a self-advancing film cassette described in U.S. Pat. No. 4,832,275. A spool 2 rotatably contained in a cassette shell (not shown) has a film 1 wound on its outer periphery to form a film roll 3. Further, the film roll 3 has a pair of restriction rings 5 and 6 fitted to the outermost peripheral surface thereof out of the vertical relative to the film roll 3 in order to restrict the loosening of the film roll 3. The distance between the pair of restriction rings 5 and 6 is large in the vicinity of a film port 9 provided with a film passage mouth (not shown). so that a film leader end la can pass therethrough. These restriction rings 5 and 6 are engaged in slant grooves formed in the inner wall of the cassette shell. Also, a pair of separation claws 7 and 8 are provided integrally on the film port 9 so as to contact the outermost peripheral surface of the film roll 3.
When the spool 2 is rotated in the unwinding direction, the film roll 3 is loosened a little if there is a tiny gap between the restriction rings 5 and 6 and the outermost peripheral surface of the film roll 3. However, the loosening of the wound film is restricted immediately by the restriction rings 5 and 6, and the film roll 3 and the restriction rings 5 and 6 are rotated together with the spool 2 thereafter. When the film leader end 1a reaches a position close to the film port 9, it is separated from the film roll 3 by the separation claws 7 and 8, and the film leader end la is advanced outside the cassette shell through the film passage mouth.
A self-advancing film cassette described in U.S. Pat. No. 4,834,306 is constructed such that ring-shaped rims are provided on the peripheral edges of a pair of flanges disposed on a spool. The rims receive the side edge of the outermost periphery of the film roll so as to prevent loosening of the film. Further, a pair of triangular separation claws are disposed to the film port such that the front ends thereof are engageable with the film leader end, and the side edges thereof push the pair of flanges outwardly to relieve the film from the restriction of the rims, so that the film leader end separated from the film roll is guided to the film passage mouth.
In general, the film leader frequently is stuck to a film portion thereunder for a number of reasons. For example, the film curls after being stored for a long time in the cassette. Also, the film may be withdrawn from the cassette under conditions of high temperature and high humidity or static electric charge. Further, withdrawal of the film from the cassette may be difficult because of difficulties during transportation of the cassette. In such case, in the aforementioned conventional self-advancing film cassette, it becomes impossible to separate the film leader surely from the film roll to advance the film from the film passage mouth. Also, it happens sometimes that only one of the separation claws separates the film leader, but the other fails to do so. In that case, as the film leader clogs the film passage mouth, if the spool keeps rotating, the film jams within the cassette shell.